The present invention relates to a metallic support for exhaust gas catalysts of Otto-engines.
Catalyst supports of ceramic material as well as of (steel) sheet metal plating are known as supports for the exhaust gas catalysts of Otto-engines. The metallic supports are preferably used in proximity of the engine in order to assure a rapid actuation of the catalyst, i.e., a rapid reaching of the reaction temperature. They consist in general of wound or stacked layers constructed like corrugated paper board. The connection of the layers takes place generally by brazing, however, it is not very stable because the brazing solder must resist the high temperatures in proximity of the engine. Only very few brazing solders are suitable for this purpose. A further difficulty resides in uniformly coating with the catalyst both the parts wetted with the brazing solder as also the non-wetted parts. It is also known to manufacture metal supports in which the layers are not soldered or brazed together with each other. Undular-shaped sheet metal panels are thereby stacked slightly staggered with respect to one another and enclosed externally. However, this solution is unstable, produces more counter-pressure with the same ratio between through-flow cross section and catalyst surface than the brazed supports and wears rapidly by reason of the vibrations occurring in engine operation. A further disadvantage of the prior art metal supports resides in that a permanent connection of the support with the catalyst housing is possible only with very large expenditures.
The object of the present invention resides in providing a metallic catalyst support which can be manufactured in a simple manner, offers a uniform coating surface for the catalyst and therebeyond can be easily and reliably secured in the catalyst housing.
The underlying problems are solved according to the present invention by the use of a partial composite laminate body as support for exhaust gas catalysts of Otto-engines which is provided with a large number of axially extending channels and made by expanding a large number of layers.
Metallic partial composite laminate bodies which can be used as catalyst support and are made by expanding as well as the basic method steps involved in their manufacture are known as such.
A large number of sheet metal layers or laminations, in general 10 to 150 are stacked one above the other for the manufacture of the expanded partial composite laminate body. At least one side of each layer is printed with a paste in a pattern that corresponds to the subsequently expanded areas. The areas in which the layers are to be connected with each other remain free of paste. The paste thus acts as separating agent which prevents the welding of the layers. The sheet metal layers or laminations stacked one above the other and provided with the paste print are now rolled one upon the other. As a result of the very strong plastic deformation during the rolling (50 to 60% cross-sectional reduction), a cold-welding takes place between the areas of the sheet metal panels which are not provided with the paste. Subsequent to the welding, the composite laminate body is heated, the paste disposed between the metal layers evaporates, and the resulting gas pressure expands the non-welded walls. Owing to the welding, the resulting channels possess a uniform surface which is not contaminated with brazing solder. Problems as regards adhesion of the catalyst, respectively, of the wash coat layer on different material surfaces therefore no longer exist, and therebeyond a welded connection is also more mechanically resistant than a brazed connection. The connecting seams of the individual layers are each offset with respect to the next layer. Depending on the degree of offset, the channels may possess in cross section the form starting from flat diamonds over squares to upright diamonds. A material which is corrosion-resistant under the planned use conditions, must be utilized as material for the individual layers; in general, one will come back to steel sheet metal plating. The wall thickness of the channels of the expanded partial composite laminate body can be kept extraordinarily low by reason of the manufacturing method, for example, within the range of 0.01 mm. The handling of such thin sheet metal panels would practically not be possible for the purpose of brazing. The manufacture of the expanded partial composite laminate bodies takes place in such a manner that the body includes two mutually oppositely disposed, axially extending non-expanded edge portions. These non-expanded edge portions can serve with advantage as fastening flange, for the body in the catalyst housing because a very safe fastening and at the same time a very uniform force introduction is possible by way of the same.